Upgrading/ Expanding in the new world (Promise)

[Osglith]

We have a medium sized XSAN for video production (21TB using six XServe RAIDs, everyone is running the latest version of XSan. We have four MacPros for Final Cut, two MacPros for graphics. An old G5 XServe for DNS and OD, Two MDC XServes - my secondary MDC is acting as the LTO-4 backup server, one Final Cut Server XServe also my AFP/SMB share, and one cluster controller). When I did all the calculations and research to build our XSAN (two years ago) you added bandwidth by adding RAID cards on your targets ( rule of thumb was 80MB/s per XServe RAID card times 2 cards per XSR). Now that we only have the Promise units available I am finding it hard to get any numbers. So I turn to you smart people for help. Storage space isn't the real issue. What I'm concerned about is integrating the new Promise arrays with my existing hardware, and how to calculate the bandwidth (I need 6-8 DVCPRO HD streams plus some pad).

Apple has recommended I build this out as a second volume due to the Promise arrays being 4Gb fiber (plus my switch and MacPros). I know I could add a zone to my fiber switch to keep the 4Gb and the 2Gb traffic separate. This seems like it would add some headaches in that the users would have two volumes mount on my edit suites (you know they will get confused as to where they put files, but also on the technical side I would have to use one fiber port for each of the two volumes, instead of the failover or "Round Robin" setup we have now (As it stands now my edit stations have two ports connected to the switch, but my graphic stations only have one - guess I have to install some more fiber cables if I go this route).

I know I'm not the only person out there who is looking at this. Anyone seen anything out there to help me in my planning (or can offer any input)?